1. Field of the Invention
The present invention relates to an apparatus that is designed for detachable attachment to a screw driver so as to successively feed screws thereto one by one, wherein the screws are held in a row and along a screw-carrying belt. Particularly, a mechanism for intermittent and regular feed of the screws will be so improved that the apparatus is rendered smaller in size, lighter in weight and more convenient to use.
2. Prior Art
Each apparatus of this kind usually has a cylindrical casing to be mounted on the distal end of an electrically-actuated screw driver, and a slider fitted in and reciprocating fore and aft in the cylinder. A coiled spring is also disposed in the cylinder so as to urge always the slider forwards and towards its home position. A screw feeding mechanism incorporated in the apparatus is of such a structure that a screw-carrying belt will be caused to intermittently advance through and relative to the apparatus. The belt will move in a direction perpendicular to said apparatus, and intermittently by a pitch at which the screws are held on the screw-carrying belt. In use, the slider will be pressed at first against an article into which the screws have to be screwed and fastened. Due to and subsequent to this initial step, the slider will be forced back deeper into the casing against the spring, thereby actuating the belt feeding mechanism to cause the belt to advance one pitch. Thereafter, the driver bit of the electric driver will immediately start to screw into the article the screw which has just been brought into alignment with the driver bit.
In general, the screw-carrying belts used in connection with the described screw-driving apparatuses do each comprise two series of cutouts formed along both the opposite lateral sides of the elongate belt. The cutouts are located at the same pitch as that at which the screws are held on said belt at regular intervals. Corresponding to these intervals, a pair of drive sprockets have a set of teeth that arranged around each of them to engage with those cutouts so as to drive the belt linearly. Since the shafts of those drive sprockets must not interfere with the driver bit, they have had to be offset sideways therefrom (for instance, "up or down" as seen in FIG. 1) or to be bored longitudinally of those shafts. In any case, such prior art apparatuses have been much complicated in structure.
A proposal made probably in view of these drawbacks is disclosed in the specification of the U.S. Pat. No. 5,284,074 as shown in FIGS. 10 and 11. This apparatus provides a mechanism whose single sprocket 103 engages with only one row of cutouts 73 that are formed in and along one lateral side of a screw-carrying belt 70. A drive shaft 104 of such a sprocket 103 extends in parallel with a driver bit 107 so that not only a slider 102 but also a cylindrical casing 101 therefor are enlarged and thus the apparatus would comparatively be rendered less convenient to manually operate. An elongate cam groove 105 with which a sliding pin 106 protruding from the casing 101 engage is formed in the shaft 104 so as to cause the sprocket 103 to intermittently rotate. Such a drive shaft however tends to be worn out soon, in particular in a case wherein it is made of aluminum for making lighter in weight the apparatus. If a hardened steel is used to form the shaft 104, then the apparatus will become heavier and less easy to operate.